Body plans are coordinated to optimize biological function


Animals are multi-cellular, eukaryotic heterotrophs



  • Most ingest organic materials
    • consume, breakdown internally with enzymes


  • Lack structural support from cell walls
    • extracellular proteins connect and strengthen cells
    • most abundant are collagen (not found in plants/fungi)


  • Cells organized into tissues
    • similar cells acting as a functional unit
    • muscle & nervous tissue allows animals to move


  • Body plan = programmed development driven by evolution

Embryonic development key for animal diversity


  • Fertilized zygote undergoes cleavage
    • mitotic cell divisions without cell growth
    • rapid division but overall size stays same


  • Early multicellular stage called a blastula (hollow ball)
    • protostome vs deuterostome = alignment of cells


  • Germ layers develop in next stage (gastrulation)
    • develop into body parts


  • Many animals have larval and adult stage
    • larva are sexually immature
    • larva look, live and eat differently

Protostomes vs Deuterostomes and the blastopore





  • Blastopore: opening of central cavity of an embryo


  • In most animals a second opening forms at opposite end
    • become openings of digestive tube


  • Protostomes: blastopore becomes mouth
  • Deuterostomes: blastopore becomes anus

Germ layers (primary cell layers in development)



  • Sponges (0), Diploblasts (2), Triploblasts (3)
    • germ layers develop into tissues and organs


  • Ectoderm:


  • Endoderm:


  • Mesoderm:



  • Coelom:

Body Cavities in Triploblasts




  • Fluid/air spaces between mesoderm layers
    • digestive track and body wall


  • Body cavity called coelom
    • cushions organs
    • fluid resistance for muscles
    • allows organs to move independently


  • Not all triploblasts have a coelom

Mammals develop subdivided body cavities from coelom




  • The dorsal cavity and the ventral cavity are the largest body compartments.


  • Dorsal body cavity includes the cranial cavity, enclosed by the skull, and the spinal cavity, enclosed by the spine


  • Ventral body cavity subdivided into 2 compartments
    • vental contains the lungs and heart
    • abdominopelvic contains the kidneys, ureters, stomach, intestines, liver, gallbladder, pancreas, bladder, anus and reproductive system

Form and function in biology


Evolution of animal size and shape




  • Animal body plans are expressions of the genome, but the product of millions of years of evolution


  • Animals body plans are constrained by physical laws
    • diffusion, movement, heat exchange
    • gravity


  • Example: Properties of water and animal shape
    • water more dense = surface bumps cause drag
    • natural selection favored tapered smooth bodies
    • convergent selection across aquatic mammals

Example: Diversity of bird form


Movie monsters are mostly not possible…. Godzilla


  • At that size, his heart wouldn’t be able to pump blood to his brain.


  • His brain would send messages too slowly to his muscles, so he wouldn’t be able to move properly


  • He’d either have to spend all his time sunbathing to stay warm

Exchange with environment limits animal bodies



  • Animals must uptake nutrients, lose waste and exchange gases
    • occurs across plasma membrane of cells


  • Simple internal body plan: Hydra
    • body wall and cavity open to environment
    • gastrovascular cavity

Exchange with environment limits animal bodies



  • Animals must uptake nutrients, lose waste and exchange gases
    • occurs across plasma membrane of cells


  • Body plan optimized for surface area: tapeworms
    • thin, flat shape
    • lots of outer cells exposed to environment

Exchange with environment limits animal bodies



  • Animals must uptake nutrients, lose waste and exchange gases
    • occurs across plasma membrane of cells


  • Many animals (like humans) have more complex internal bodies
    • reduces total # of cells on outer surface
    • volume > surface area
    • ‘think’ whale versus flea


  • Internal structures for exchange evolve…
    • highly branched or folded

Exchange with environment limits animal bodies



  • Animals must uptake nutrients, lose waste and exchange gases
    • occurs across plasma membrane of cells


  • Many animals (like humans) have more complex internal bodies
    • reduces total # of cells on outer surface
    • ‘think’ whale versus flea


  • Internal organs for exchange evolve…
    • highly branched or folded
    • digestion, respiration and circulation
    • fluids connect structures to other cells

What are the advantages of a complex body plan?



  • External skeleton?


  • Sensory organs (eyes, ears, etc.)?


  • Internal digestion organs?


  • Specialized filtration systems?



  • How do internal systems allow life on land?

Hierarchy of animal body plans



  • Cells with similar function grouped into tissues


  • Different tissues organized into functional units: Organs


  • Groups of organs can work together: Organ systems


  • There are a limited set of cells and tissues
  1. epithelial:
  2. connective:
  3. muscle:
  4. nervous: